In the world of physical chemistry, aerosols are defined as systems of colloidal particles dispersed in a gas. When the gas is the Earth's atmosphere, many of the particles originate from man-made events that generate smoke, smog or dust. Human and animal populations can experience medical problems when such particles are prevalent in high concentrations. As is known in the art, larger aerosols settle/land more quickly than smaller aerosol particles that can travel for hundreds or thousands of miles. Accordingly, atmospheric science attempts to monitor local atmospheric regions as a means to monitor local aerosol generation as well as “imported” aerosols. Monitoring can be part of pollution awareness, pollution regulation, scientific research, etc.
Devices that measure aerosol concentration and size distribution include systems that draw air through a filter and then analyze material left on the filter. However, these systems are complicated and expensive. Other types of devices that can be used for aerosol measurement are photometers where the aerosol measurement process is known as sun photometry. Scientific grade photometers are designed to make direct sun measurements and measurements of the surrounding sky. The direct sun measurement can be used to make what is known as a Langley plot to determine solar intensity as an indicator of total aerosol attenuation. The sky measurement is used to determine sunlight scattering due to the presence of aerosols. Both of these measurements can be made at several discrete wavelengths using colored filters. Typical scientific-grade sun photometers are two-telescope devices (i.e., one used for direct sun measurements and one used for sky measurements) that are fairly complex and expensive. Thus, measurement of aerosol concentration and size distribution in an atmospheric region tends to be limited to well-educated and well-funded groups.